Theses (Electrical Engineering and Computer Science)http://hdl.handle.net/1957/81632014-10-23T17:56:24Z2014-10-23T17:56:24ZPosition estimation in indoor localization systemQiao, Tianzhuhttp://hdl.handle.net/1957/531992014-10-22T20:22:44Z2014-09-18T00:00:00ZPosition estimation in indoor localization system
Qiao, Tianzhu
Indoor positioning systems can be used for many applications such as indoor navigation,
emergence response, asset monitoring, and shopper assistance. Due to the weak received signal and multipath reflection, the global positioning system (GPS) generally does not work in indoor environments. There are a variety of radio frequency (RF) signals and systems available for indoor localization, e.g., radio-frequency identification (RFID), cellular network, Bluetooth, WiFi, and ultrawideband (UWB) systems. For high-precision localization using RF signals, commonly used techniques include time-of-arrival (TOA) and time-difference-of-arrival (TDOA). Although various aspects of TOA and TDOA systems have been studied extensively, new techniques are still needed to improve two key position estimation aspects: accuracy and complexity.
In the first part of this dissertation, we focus on position estimation methods assuming line-of-sight (LOS) propagation. Anchor layout is an important area that affects localization performance. Generally the Cram\'{e}r-Rao lower bound (CRLB) can be used to find the optimal anchor layout. However, it is computationally expensive and not suitable for fast deployment. We propose an incremental anchor layout method (ICALM) based on the largest range measurement change criterion, which is very easy to implement.
For TOA systems, an improved method of moments (IMOM) algorithm is proposed to improve the estimation accuracy at the expense of a slightly increased computational complexity. For TDOA systems, we propose a maximal likelihood (ML) based coarse position estimation method to provide the initial position for the nonlinear least squares (NLLS) method. The goal of this proposed method is to substantially increase the stability of the NLLS method. In order to reduce estimation complexity, we propose a nonlinear expectation maximization (NLEM) based estimator. This estimator transforms the high-dimensional estimation problem into several 1-dimensional problems, which does not need any matrix manipulations and is much simpler to implement than the NLLS and ML methods.
In practice, none-line-of-sight (NLOS) links often exist. In the second part of this dissertation, we focus on methods for NLOS mitigation. When all the range measurements suffer from severe NLOS errors, no methods could work well without additional information. However, when only part of the range measurements suffer from NLOS propagation, and the LOS range measurements are sufficient for position estimation, it is possible to improve the accuracy without any \emph{a priori} information. We propose an improved least median squares (ILMedS) algorithm, which uses the residue to weight all the anchors and adaptively searches for the largest group of the reliable links for final estimation. It greatly decreases the probability of reaching the outliers and increases the accuracy. At the same time, all the methods developed for the LOS scenarios can be directly applied as the core estimator.
Since ILMedS needs to calculate a location estimate for each subset, its computational complexity is high. We propose a particle filter based position estimation (PFPE) method for NLOS mitigation, which uses particles to represent the potential target. Each particle utilizes the range measurements to update its position. It is much easier to implement than the ILMedS method, while their performances are very similar.
Graduation date: 2015
2014-09-18T00:00:00ZEfficient use of time information in analog-to-digital convertersHu, Yuehttp://hdl.handle.net/1957/525532014-10-01T18:42:11Z2014-07-25T00:00:00ZEfficient use of time information in analog-to-digital converters
Hu, Yue
Time-domain data conversion has recently drawn increased research attention for its highly digital nature in favor of process technology scaling. Also, as the time information being carried by binary voltage, time-domain operation is much less sensitive to voltage noise compared to conventional voltage domain operation. However, for analog-to-digital converter (ADC) application, the challenge lies in the methodology of benefiting from time-domain operation while maintaining/improving the overall data conversion accuracy and power efficiency. This dissertation has a focus on the investigation of novel data conversion topologies based on classic voltage domain operation that is capable of generating time information, to improve ADC resolution, system stability and speed without power penalty.
In the first approach, a novel continuous-time (CT) delta-sigma modulator (DSM) using a time-interleaved quantizer is proposed and implemented. Along with the doubled sample rate, the proposed architecture utilizes time information to perform correlated coupling between the two quantizer channels. A 120MS/s CT ΔΣ ADC using proposed technique is implemented in 0.18µm CMOS process. The measurement results achieve second order noise coupling from the interleaved quantizer itself without extra phases. More importantly, excess loop delay of two full sample clocks is compensated by time-domain signal coupling; the resulted CT DSM is fully stabilized in 120MHz sampling rate and achieves 11 effective number of bits (ENOB).
In the second approach, a new category of pulse-width-modulation (PWM) scheme is proposed and described: time symmetric PWM (TSPWM). An ADC structure is further proposed and implemented utilizing this novel voltage-to-time converter, followed by a first order noise-shaped switched-ring-oscillator (SRO) TDC quantizer. This ADC topology takes advantage of the TDC speed scaling for its digitized operation to boost the overall ADC resolution and signal bandwidth, while the voltage-to-time front-end is able to remain at a much lower speed than the TDC, thanks to the proposed technique. This is the first work that decouples the PWM modulation rate from TDC quantizing speed without distortion penalty. Built in 0.18µm, the implemented ADC is able to sample at a range from 20MHz to 40MHz, the generated pulse train is quantized by the following SRO TDC at a rate of 400MHz. The prototype chip shows a SFDR improvement over 24dB on the ADC output when TSPWM is used.
Graduation date: 2015; Access restricted to the OSU Community, at author's request, from Sept. 30, 2014 - Sept. 30, 2016
2014-07-25T00:00:00ZMaterial development for thin-film transistorsArchila, Kevin Alexanderhttp://hdl.handle.net/1957/524772014-09-29T22:55:47Z2014-09-25T00:00:00ZMaterial development for thin-film transistors
Archila, Kevin Alexander
The focus of this thesis is developing materials for thin-film transistors (TFTs).
Cu₃SbS₄ is explored as p-channel layer. Cu₃SbS₄ TFTs show p-type, depletion-mode
behavior with a small amount of gate-controlled modulation of the channel conductance.
This behavior is consistent with Hall measurements indicating a mobility of
17 cm²V⁻¹s⁻¹ and hole carrier concentration of 10¹⁷ cm⁻³. Simulations employing
the comprehensive depletion-mode model (CDMM) are used to extract TFT channel
interface and bulk mobility, along with carrier concentration. The extracted values
from CDMM simulations are in close agreement with Hall-effect measurements of
carrier concentration and TFT incremental mobility.
TFTs are fabricated employing solution-processed thin films spin-coated with
electrochemically prepared solutions. Dual active-layer TFTs utilizing solution-processed
IZTO-IGZO active layers demonstrated the highest average mobility, exceeding that
of control sputtered IGZO TFTs.
Sputtered IGZO TFTs are studied using solution-processed Al₂O₃ and LaAlO₃
gate insulator layers. The solution-processed Al₂O₃ gate exhibits high subthreshold
swing compared to employing a thermally grown SiO₂ gate insulator layer.
Graduation date: 2015
2014-09-25T00:00:00ZSimplified WECC modeling for frequency response, wind integration, and energy storageBhattacharji, Pranathihttp://hdl.handle.net/1957/523692014-09-26T16:23:35Z2014-09-11T00:00:00ZSimplified WECC modeling for frequency response, wind integration, and energy storage
Bhattacharji, Pranathi
The primary objective of a grid is to maintain a balance between generation and load. If these quantities are not in balance with each other, severe damages such as voltage fluctuations, low power quality, power outages or even cascaded blackouts may occur. Hence one of the primary factors that holds the grid together and makes it operative is the frequency. Thus maintaining the frequency within certain limits is the basic operational requirement. Lately, the power system's dependency on wind power has increased, suggesting that wind power generation is expected to contribute its services which are normally delivered by conventional power plants. However a system that has high wind penetration results in reduced system inertia due to the wind turbine's lack of droop characteristics that may lead to frequency control issues. Thus a backup system is needed such as an energy storage system that can be controlled to supply energy when demand is high i.e., during demand response operations, energy can be stored by increasing load and temperature, and energy can be effectively returned by reducing load and temperature. This thesis presents the modelling of such an energy storage system which consists of several generators responding at different time scales and several water heaters that can be controlled based on the frequency deviation from its nominal value. The ultimate goal of this paper is to perform transient analysis on a simplified Western Electricity Coordinating Council (WECC) system for frequency response, wind integration and energy storage using primary frequency control and secondary frequency control. Simulation results will showcase the frequency excursions of the WECC system with and without energy storage under normal loss of generation event and under wind penetration.
Graduation date: 2015
2014-09-11T00:00:00Z